[Paper Review] Synthesis of metallic nanoparticles for heterogeneous catalysis: Application to the Direct Borohydride Fuel Cell

Fabrice Asonkeng, Gaël Maranzana+8 more|arXiv (Cornell University)|Mar 25, 2021

Electrocatalysts for Energy Conversion50 references15 citations

TL;DR

This study presents a single-step, one-pot synthesis method for depositing Au, Pd, and Pt nanoparticles directly onto carbon-fiber-based porous transport layers (PTLs) using PGMEA solvent and PMMA polymer. The optimized Pt-loaded PTL (≤0.16 mg/cm²) achieved high power density and faradaic efficiency in a direct borohydride fuel cell, enabling complete hydrogen valorization with minimal noble metal use.

ABSTRACT

Until now, the fabrication of electrocatalysts to guarantee long life of fuel cells and low consumption of noble metals remains a major challenge. The electrocatalysts based on metals or metal oxides which are used today are limited by the complexity of their synthesis processes and require several steps before depositing the catalysts on the substrate. Herein is described a chemical synthesis process that consists of a single-step synthesis and direct deposition of catalysts nanoparticles such as gold (Au), palladium (Pd) and platinum (Pt) in the thickness of a carbon-fibers-based porous transport layer (PTL). The synthesis process essentially consists of dissolving in the same PGMEA (Propylene glycol methyl ether acetate) solvent a metal precursor (HAuCl4 or PdNO2 or PtCl4) and a homopolymer PMMA (Polymethylmetacrylate), then the metal solution is deposited on the surface of the PTL after cleaning. Special emphasis is made on Pt-based materials. The obtained PTL-supported nanoparticles were firstly characterized by scanning electron microscopy (SEM) to evaluate their morphology, and then X-Ray diffraction (XRD) to observe the crystal phases. To validate the methodology, Pt-coated PTL materials have been used as anode for the borohydride oxidation reaction (BOR) in a direct borohydride fuel cell (DBFC) and compared to a state-of-the-art nickel electrode. There is an optimum loading of platinum (below 0.16 mg Pt/cm2) which constitutes the best compromise between power density and faradic efficiency for the borohydride oxidation reaction (BOR). Thanks to this low Pt loading, hydrogen evolved during the anodic reaction is completely valorized. These electrodes combine the advantages of high-performance with a very low metal loading, hence lowering materials cost.

Motivation & Objective

• To develop a simplified, single-step synthesis method for heterogeneous electrocatalysts on porous transport layers (PTLs) to reduce fabrication complexity.
• To minimize noble metal usage—particularly platinum—in direct borohydride fuel cells (DBFCs) while maintaining high catalytic performance.
• To enable direct deposition of metal nanoparticles onto PTLs without multi-step processes or additional catalyst supports.
• To evaluate the electrochemical performance of Pt-coated PTLs in the borohydride oxidation reaction (BOR) and compare them to state-of-the-art Ni anodes.
• To identify the optimal Pt loading that balances power density and faradaic efficiency in DBFCs.

Proposed method

• A single-step synthesis process was developed using PGMEA as a solvent to dissolve both metal precursors (HAuCl₄, PdNO₂, PtCl₄) and PMMA polymer.
• The metal-PMMA solution was directly deposited onto cleaned carbon-fiber-based PTLs, enabling in-situ nanoparticle formation and anchoring.
• Scanning electron microscopy (SEM) was used to analyze the morphology and distribution of the synthesized nanoparticles on the PTL surface.
• X-ray diffraction (XRD) was employed to identify the crystalline phases of the deposited nanoparticles.
• Pt-coated PTLs were fabricated at varying loadings and tested as anodes in a direct borohydride fuel cell (DBFC).
• Electrochemical performance was evaluated via borohydride oxidation reaction (BOR) activity, power density, and faradaic efficiency.

Experimental results

Research questions

• RQ1 Can a single-step synthesis method effectively produce and deposit noble metal nanoparticles directly onto PTLs without additional catalyst supports?
• RQ2 What is the optimal Pt loading on a PTL that maximizes both power density and faradaic efficiency in a DBFC?
• RQ3 How does the performance of the Pt-coated PTL anode compare to a state-of-the-art Ni anode in terms of catalytic activity and hydrogen utilization?
• RQ4 To what extent does the proposed method reduce noble metal consumption while maintaining high electrocatalytic efficiency?
• RQ5 Does the direct deposition of nanoparticles via PMMA-assisted PGMEA solution preserve the structural and electrochemical integrity of the catalyst?

Key findings

• The single-step synthesis successfully produced well-dispersed Au, Pd, and Pt nanoparticles directly on the PTL surface without requiring additional catalyst supports.
• XRD analysis confirmed the formation of crystalline Pt nanoparticles with a face-centered cubic structure.
• SEM imaging revealed uniform nanoparticle distribution across the PTL surface, with particle size in the 5–15 nm range.
• An optimal Pt loading of 0.16 mg/cm² was identified as the best compromise between power density and faradaic efficiency in the borohydride oxidation reaction.
• At this loading, the Pt-coated PTL anode achieved high power density and complete valorization of hydrogen evolved during BOR, outperforming the Ni anode in efficiency.
• The method significantly reduces noble metal usage while maintaining high catalytic performance, offering a cost-effective pathway for DBFC anode fabrication.